I peeked at the code, so there's basically two major variations on that scene, and it depends on one things: Did Emma already have a threesome with Marcus and Sophia?
Variation 1: Emma already fucked Marcus, you end up in a scene with fewer choice options. You're given the option to stop Marcus, you don't get to pick if you jerk off or not, and after Marcus and Emma go at it you're given the option to go for sloppy seconds, or wuss out. However, if your confidence score is LESS than -30, then you just wuss out, as the other option is greyed out.
Variation 2: Emma did NOT fuck Marcus before, you have a scene with more choices, but some of them might be locked based on your confidence score. If your confidence is HIGHER than -20, you get the option to stop Emma before she gives Marcus a BJ. This leads to a scene where Emma sucks you off. After Emma starts to suck Marcus, you get another choice, where if your confidence is LESS than -30, you can jerk off while watching. If you don't jerk off, the scene ends after Emma takes the blind fold off and sees that it's Marcus, she kicks him out of the room, you two agree not to talk about it and go back to the party. If you DO jerk off, Emma gets turned and Marcus proceeds to try and fuck her while you watch. At this point, Emma will ask you "Last chance to back out Philip" but the game doesn't actually show the choice, it just check your confidence score without telling you. If your score is LOWER than -50 then Emma will fuck Marcus while you watch, and then you and Marcus bukkake her face. If your sore is HIGHER than -50 then MC will say "No, I don't like it" and then Emma stops the scene.